Electric motors are used in devices that range from small appliances and electronic devices to large motors for pumps and factors. Motors are one of the world's largest consumers of electricity, but are traditionally either very inefficient or very expensive. Energy efficiency for a motor refers to how much of the electrical energy input is converted to work output from the motor. Small appliance motors in the home traditionally have an efficiency slightly better than 50 percent. Large motors for pumps and factories often have efficiencies in excess of 90 percent, but are very expensive. Linear motors move equipment at high speeds and actuate along one axis, while rotary motors turn a shaft and often are geared to trade speed for torque.
Traditional motors use magnet wire wound around steel to create a stator. The magnet wire is typically a thinly coated insulator over a conductor of copper, aluminum, or other metal, which produces a controllable electromagnet. Typically, the stator includes different magnetic arrays. The windings can be mechanically or digitally switched to align the fields of the magnetic arrays, where the stator generates an electromotive force by timing the changes in magnetic flux.
In a traditional motor, the stator often consists of multiple windings insulated by paper, enamel, or some plastic such as polyimide films that are usually thin to allow maximum current capabilities in relationship to the available volume of conductor. Making the insulation thicker to prevent shorts between windings would both decrease the amount of available conductor in a pole with a fixed volume available for windings, and increase the resistance of the stator windings. Motor efficiency increases as losses decrease, but the motor losses increase proportional to the square of the current multiplied by the resistance. Thus, increased winding resistance decreases motor efficiency. Additionally, traditional dielectrics or wire coatings for magnetic wire are good thermal insulators, which means increased coating thickness operates to increase the retention of heat in the wire. The thermal performance of wire coatings creates a contradiction in performance, where increasing the thickness allows higher voltages, but promotes overheating. Thin wire insulation is a major cause of motor failure in traditional designs, and overheating limitations define motor system performance envelopes.
FIG. 1 illustrates a diagram of a cross section of a traditional motor with coils wrapped around steel laminations. An example of a motor 100 can include four or six coils 130 (six coils are shown) wound around steel laminations 120 with the magnetic circuit representative of a standard arrangement for linear or rotary motors. Center 110 is a center of rotation for motor 100, and can be the location of a rod or shaft. The use of back iron behind the permanent magnets to complete the magnetic circuit and laminations in the armature core to increase the field strength at the gap improves performance, but has intrinsic weight, cost, eddy current, and hysteresis loss penalties. The relatively low number of magnetic poles in both the rotor and stator contribute to high torque ripple. The large amount of steel increases the field strength, but has high eddy current and hysteresis losses, while making motor 100 heavy.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein.